Technical Field
This application relates to the field of antennas, in particular, to circularly polarized or dual polarized antennas in the form of air-filled patch antennas.
Description of the Related Art
Since circularly polarized (CP) and dual polarized antennas are able to receive EM wave with an arbitrarily oriented linear polarization, they have been widely used in many applications such as RFID (Radio Frequency Identification) readers, GPS (Global Positioning System) and satellite communication systems. Dual polarized antennas can independently receive and transmit electromagnetic waves polarized in two orthogonal directions. The two polarized electromagnetic waves can carry two independent signals. Therefore, they are widely used in wireless base stations.
Taking the advantages of low profile and light weight, the patch antenna is one of the most popularly used antennas. A CP patch antenna can be easily realized by printing a metal patch on a piece of grounded dielectric substrate. To reduce the dielectric loss, to improve radiation efficiency and to cut the manufacturing cost, air-filled CP and dual polarized patch antennas are frequently used by supporting the metal patch with dielectric posts. Such dielectric supporters inevitably incur extra losses, cost and inconvenience in installation for mass production. Another widely used CP antenna is the slot antennas with metal cavities, among which CP antennas can be created by various slot arrangements. Usually, the metal cavities usually expensive to make and is very bulky. CP dielectric resonator antenna (DRA) is also a kind of well-known CP antennas. With the high permittivity of the dielectric, the volume of the antenna can be greatly reduced. However, the price for low-loss dielectric is usually very expensive. For many practical applications, it is desirable to have a type of CP or dual polarized antennas that are of low profile, low cost, light weight, and convenient to make.